1. Field of the Invention
The present invention relates to inverters of the type operable to invert low voltage DC power, such as but not limited to the type commonly employed in vehicle power systems, into AC power sufficient for powering consumer electronic devices.
2. Background Art
In recent years, a 120 Vac/230 Vac power supply for consumer electronics devices in vehicles has become a basic feature in automotive industry. In some applications, the power source of the 120 Vac/230 Vac supply is from a 12 Vdc vehicle battery. Usually, the 12 Vdc is first stepped-up to a higher level dc voltage, such as 170 Vdc/340 Vdc, and then it is inverted to a modified sine wave AC voltage. The power rating of this 120 Vac/230 Vac power supply may be up to one kilowatts. A typical circuit configuration for an inverter 100 is shown in FIG. 1.
In FIG. 1, a step-up converter 102 is shown as a push-pull converter, having one of a full bridge or central tapped rectifier 104, and an output inverter 106 is shown as an H-bridge. Each of the converter 102 and the inverter 106 includes switching devices 108, 110 that must be selectively activated and deactivated in a manner suitable to stepping-up and inverting the DC supply 1 12. Separate push-pull and H-bridge controllers 114, 116 may be used to output time varying signals to selectively activate and deactivate switching components 108, 110 of the converter 102 and inverter 106. These time varying signal may be fed to driver circuits 120, 122 that in turn coordinate activation and deactivation of a selected one or more of the switching devices 108, 110.
Importantly, two separate auxiliary power supplies 126, 128 are used for each of the controllers 114, 116. One of the power supplies 126 is a voltage regulator, such as a linear regulator, that regulates the battery voltage to a voltage suitable for powering the controller 114 and drivers 120. The other one of the power supplies 128 is an isolated, switch mode power supply (SMPS) that electrically isolates the second stage of the inverter from the primary stage. It may include a power transformer (not shown) to facilitate electrically isolating power supplied to the gate driver 122 and controller 116 relative to the power provided to the primary stage.
The use of the SMPS 128 to electrically isolate the primary stage from the secondary stage is advantageous in preventing the higher voltage secondary stage from interfering with operations of the primary stage. Isolated SMPS, however, are large in size and relatively expensive in design due to use of components having greater power ratings, like the power transformer.